A die bonder is an apparatus that picks a semiconductor die from a supply of semiconductor dies (e.g. a wafer tray) and places it on a semiconductor die carrier (e.g. a leadframe). Such a process is known as die bonding. The die bonder comprises two important modules: i) a bondhead for transferring and bonding the semiconductor die to the semiconductor die carrier and ii) a workchuck for supporting the semiconductor die carrier during the die bonding process. To ensure the quality and reliability of the die bonding process, the bondhead and the workchuck should be mutually aligned. Accordingly, the surfaces of the bondhead and the workchuck facing each other should be parallel to each other before the semiconductor die carrier is placed on the workchuck for die bonding. During die bonding, a bonding surface of the semiconductor die is pressed by the bondhead against the semiconductor die carrier with a designated force and under a certain temperature profile. Since the bonding surface of the semiconductor die includes many solder or gold bumps with dimensions not exceeding a few hundred microns, a small deviation of the alignment of the bondhead with respect to the workchuck (e.g. 10 microns) might result in side forces and placement error, which thereby compromises the quality and reliability of the die bonding process. Importantly thus, the alignment of the bondhead with respect to the workchuck should be maintained to ensure the quality and reliability of the die bonder.
A conventional method of determining the parallelism of the surfaces of the bondhead and the workchuck facing each other involves the use of carbon paper. The carbon paper is a thin piece of pressure sensitive paper that changes colour when pressure is applied. To determine the alignment of the bondhead with respect to the workchuck, the carbon paper is placed on the workchuck right below the bondhead. The bondhead is then moved downwards to press the carbon paper against the workchuck. Thereafter, the bondhead is moved upwards for an operator to inspect a colour pattern on the carbon paper to determine the parallelism of the surfaces of the bondhead and the workchuck facing each other, and hence, the alignment of the bondhead relative to the workchuck.
Such a method of determining the alignment of the bondhead, however, is inaccurate since the carbon paper is unable to feedback the degree of the bondhead alignment to the die bonder. Accordingly, the operator has to manually determine the magnitude of a tilt angle of the bondhead relative to the workchuck in order to adjust the bondhead position. The human intervention required in this conventional method of determining the bondhead alignment means that the desired accuracy would be difficult to achieve.
Other conventional methods may include the use of optical sensors such as autocollimators or lasers to determine the parallelism of the bondhead and workchuck at room temperature. However, these methods are not able to determine the parallelism at high temperatures (200˜400° C.) due to disturbance of air density.
Thus, it is an object of the present invention to seek to provide an apparatus and method for determining an alignment of a bondhead of a die bonder relative to a workchuck that provides higher measurement accuracy than the conventional method described above and/or minimizes the degree of human intervention. Preferably, the apparatus and method for determining the bondhead alignment can operate at high temperatures (200˜400° C.).